Assemble the vegetables: Preheat oven to 400 degrees F. Butter a 1 1/2-quart casserole or baking dish and set aside. Combine the bread crumbs, pumpkin seeds, butter, and half the thyme in a medium bowl, stir in the goat cheese, and set aside. Slice the pumpkin quarters into 1/8-inch-thick pieces and repeat with the cauliflower quarters. Combine flour, garlic, mustard seeds, salt, cumin seeds, pepper, and remaining thyme in a small bowl. Spread 1/3 of the pumpkin in the bottom of casserole and sprinkle with 2 teaspoons of the flour mixture. Repeat with 1/2 of the cauliflower and 2 teaspoons of flour. Continue layering with the remaining pumpkin, cauliflower, and flour, finishing with pumpkin on top. Pour the half-and-half over the entire casserole, place on a baking sheet, and bake in the center of the oven for 30 minutes.

Sprinkle topping: After initial 30 minutes of baking, sprinkle bread-crumb mixture over casserole. Return it to oven and bake until golden and bubbly, about 30 more minutes. Serve hot.